Wind turbine power generating apparatuses have become increasingly popular in recent years in view of preservation of the global environment. Especially, there are plans being developed in many regions, for building large wind turbine power generating apparatuses which are advantageous in improving power generation efficiency on water such as ocean and lake.
As a wind turbine power generating apparatus disposed on the water, known is a floating-body type wind turbine power generating apparatus including a wind turbine generator disposed on a floating-body floating on the water surface. In a general floating-body type wind turbine power generating apparatus, a floating-body is connected to anchors disposed on the water bottom via mooring lines so that the floating-body is moored on a predetermined position on the water. For instance, Patent Documents 1 to 3 disclose a method of towing a floating-body type wind turbine power generating apparatus which has been assembled in advance to a predetermined position on the water. Such a floating-body type wind turbine power generating apparatus is normally maintained while the floating body is moored on a predetermined position on the water.
For the purpose of facilitating maintenance works at high places, Patent Document 4 discloses a method for submerging and mounting a tower of a wind turbine power generating apparatus onto the water bottom upon maintenance. Further, Patent Documents 5 and 6 disclose a configuration in which a tower of a wind turbine power generating apparatus is submerged in a spar upon maintenance.